Elastomeric impact energy dissipator

ABSTRACT

The illustrative exemplary embodiment incorporates the elastomeric impact energy dissipating body as a bumper mount connecting an automotive vehicle collision bumper bar to the vehicle frame. The dissipator is constructed of high density polyurethane or like material having the properties of high modulus of elasticity and high tensile elongation. The dissipator has a cross sectional shape generally of rectangular tubular configuration including elongated columnar wall elements adapted to undergo laterally outward buckling under impact compression loading therein and a tensile web extending laterally between the columnar elements operative to resist the buckling up to a predetermined value, to provide large amounts of energy dissipation along with the remainder of the body during the buckling, and to elastically return the body and the supported bumper bar to its original condition following release of the impact forces.

ilnited States Patent Levering [451 Sept. 26, 1972 154] ELASTOMERICIMPACT ENERGY DISSIPATOR [72] Inventor: David R. Levering, Cincinnati,Ohio [73] Assignee: General Motors Corporation,

Detroit, Mich.

[22] Filed: July 22, 1970 [21] App]. No.: 57,214

[52] US. Cl ..293/88, 267/140 [51] Int. Cl. ..B60r 19/06, F60f1/36 [58]Field oiSearch..267/140, 141, 63, 153; 293/85, 293/88 [56] ReferencesCited UNITED STATES PATENTS 3,514,144 5/1970 I Alderfer ..293/71 R3,507,123 4/1970 Miura 61/48 1,655,777 l/1928 Weiland ..293/88 FOREIGNPATENTS OR APPLICATIONS 658,945 6/l929 France ..293/85 1,116,719 5/1956France ..267/63 1,145,861 3/1963 Germany ..267/63 PrimaryExaminer--Gerald M. Forlenza Assistant ExaminerRobert Saifer Attorney-W.E. Finken and D. L. Ellis [5 7] ABSTRACT The illustrative exemplaryembodiment incorporates the elastomeric impact energy dissipating bodyas a bumper mount connecting an automotive vehicle collision bumper barto the vehicle frame. The dissipator is constructed of high densitypolyurethane or like material having the properties of high modulus ofelasticity and high tensile elongation. The dissipator has a crosssectional shape generally of rectangular tubular configuration includingelongated columnar wall elements adapted to undergo laterally outwardbuckling under impact compression loading therein and a tensile webextending laterally between the columnar elements operative to resistthe buckling up to a predetermined value, to provide large amounts ofenergy dissipation along with the remainder of the body during thebuckling, and to elastically return the body and the supported bumperbar to its original condition following release of the impact forces.

4 Claims, 7 Drawing Figures PATENTEDSEPZS m2 SHEET 1 UF 2 ml i f llll ll I llll I NVEN TOR fla /2272 Jez/e 12129 A TTO/Q/VEY ELASTOMERIC IMPACTENERGY DISSIPATOR This invention relates to energy dissipators and moreparticularly to energy dissipating devices suitable for use inautomotive vehicle collision bumpers and similar installations requiringsubstantial impact energy dissipation followed by self-restoration ofthe device to a normal condition operative for repeated such impacts andenergy dissipation.

Desirable features of energy dissipators suitable for energy absorbingautomotive bumper installations and the like have been that the energydissipator sustain or absorb large amounts of the kinetic energyoccurring in the input excursion of the device under impact and that itnot rebound or return substantially all of such energy in its originalform to the impacted object following the occurrence as would normallybe the case in the examples of completely elastic coilv spring devices,compressible air spring devices and the like. In addition to thisrequirement of true energy dissipation or irreversible absorption, thereis often the somewhat incongruous requirement that the device beself-restoring, i.e., the device return itself and the collision bar orother impacted object to its original condition so as to receiveadditional impact energy and not be limited to so-called shot" operationrequiring replacement of the energy'dissipating modules or units.

The primary object of this invention is to meet these several criteriain a device of relatively low cost and utmost simplicity through theeffective use of the viscoelectric properties of elastomeric materials.

A further object of this invention is to provide such an elastomericenergy dissipator suitable for use in energy absorbing automotive bumperinstallations and the like wherein the dissipator is not only effectivefor the energy dissipation functions above set forth, but also isstructurally sufficient to provide support for the bumper on the vehiclebody satisfactorily in normal use conditions.

As a principal feature,the energy dissipating device of the inventiontakes the form of a body of-elastomeric material such as a high densitypolyurethane or rubber having the properties of high stiffness or highmodulus of elasticity and high elongation and being formed in agenerally rectangular tubular cross-section in which the tubular sidewalls are comprised of a pair of columnar elements and a pair ofintegrally associated base elements, with one or more tensile straps orwebs being connected integrally between the columnar elements to resista predisposed outward buckling thereof. With the device aligned to havethe columnar elements extend in the direction of expected impact thetensile web, in concert with certain factors of the shaping of thecolumnar elements themselves, dictates a force level at which the devicewill begin to deflect and undergo an energy absorbing excursion. Uponreaching such value, an outward buckling of thecolumnar elements causesthe device to foreshorten along the axis of the applied force and expandlaterally outwardly in such a manner as to predictably elongate thetensile web. The viscoelastic properties of the material of the tensileweb, in concert with the same effects in the material of other sectionsof the device to a lesser degree, provides substantial true energydissipation without rupturing of the device. Following the release ofthe predetermined impact force, however, the device retains sufficientelasticity only to efficiently restore itself to its original condition,without violent rebound, so as to be ready for operation in repeatedimpacts.

As a further feature, the device is made of sufficient thickness as topartake of the material stiffness of the particular elastomer so that,through the use of a selected number of such devices, they provide therequired primary support of the collision bumper on the vehicle.

The foregoing and other objects, features and advantages of theinvention will be readily apparent from the following specification andfrom the drawings wherein:

FIG. 1 is a front elevational view of a vehicle body having a collisionbumper bar installation including the energy dissipating device of thepresent invention;

FIG. 2 is an enlarged vertical sectional view taken generally along theplane indicated by lines 2-2 of FIG. 1;

FIG. 3 is an enlarged view taken along the lines 3-3 of FIG. 2 showingthe dissipator in normal condition;

FIG. 4 is a view similar to FIG. 3 taken along the lines 4-4 of FIG. 2;

FIG. 5 is a view similar to FIG. 3 showing the dissipator and bumper barin a deflected condition;

FIG. 6 is a partial perspective view of the collision bumper barinstallation; and

FIG. 7 is a force-deflection graph indicating the operationalcharacteristic of the dissipator.

Referring now particularly to FIG. 1 of the drawings, there isillustrated the front end portion of a vehicle body designated generallyas 10 which includes a chassis frame or subframe of conventionalcharacter. but provided with a pair of terminal end towers 12, best seenin FIG. 6. These towers are integrally associated with the vehiclelongitudinal frame rails 14 and may be further associated with a lateralcross-member, not shown. It is to be understood that while the drawingsillustrate a separate chassis frame, the invention is equally wellapplied, in the case of these bumper installations, to vehiclesemploying unibody construction.

In the exemplary vehicle bumper installation, there is included agenerally oval-shaped in elevation bumper or collision bar 16 includingupper and lower transverse portions 18 and 20 which help to define, asillustrated, an oval grille opening for exposing a vehicle grillestructure 22 affixed to the front end sheet metal portion of thevehicle. As viewed in FIGS. 1 and 2, bumper 16 is enveloped at itsrearward margins by the front end sheet metal of the vehicle includingthe two front fenders, the hood and the lower splash shield 24 in such amanner as to permit telescoping of bumper 16 into the front end sheetmetal without interference during the application of collision forcessufficient to bring the energy absorbing functions of the dissipator ofthis invention into play. Bumper 16 may be fabricated of a compositeconstruction including an inner steel backbone having molded thereover ahigh density but foam-like self-skinning polyurethane or other desiredelastomer capable of sustaining minor bumps and abrasions withoutdamage.

Referring now more particularly to FIGS. 2 and 6, the bumper 16 isrigidly mounted on frame towers 12 by a set of four energy dissipatorsconstructed in accordance with this invention, the upper pair ofdissipators being designated as 26 and the lower pair 28. With bothpairs, suitable mounting plates or flanges 30 are formed on bumper 18and towers 12 to provide flat engagement surfaces suitable for centerbolting as at 31 of the base portions of the dissipators, soon to bedescribed, flushly thereto in uniform load bearing en-' gagementcompletely across the base portions. The upper and lower pairs ofdissipators 26 and 28 are generally identical except that, asillustrated, the lower pair may be provided with a guidance mechanism 32including a pair of generally L-shaped plates each having one legthereof embedded in the elastomeric dissipator as molded, and having theother leg thereof extend over the top surface of the dissipator into amating engagement with the other plate. One plate carries a slot 34,best viewed in FIG. 3, receiving an up-turned tab 36 on the other plate.The interlocking engagement between the plates afforded thereby dictatesthat the dissipators deflect or deform in a direction extendinglongitudinally of the body so that, in the event of cornering impacts orlike forces causing displacement of bumper l6 tending toward a pathangularly disposed to such a longitudinal direction, the guidancemechanism reacts the tendency and forces it in the longitudinal path.Alternatively to such plates, swinging links or panhard rods may beemployed between the frame and bumper to restrict lateral motion of thelatter.

FIGS. 3 and illustrate the nature of the deflection or energy absorbingexcursion resulting from the configuration or shaping factors of thedissipators 26 and 28. As indicated in FIG. 2, each dissipator as moldedor fabricated in normal condition has generally the form of arectangular tubular body including elongated side wall columnar elements38 and base elements 40 integrally connected with the columnar elements.The preferred form of dissipator includes a single tensile strap or web42 extending integrally from one columnar element 38 to the other atpoints generally midway their length. Such web isseen as being definedthusly by two tube defining cavities 44 which are aligned along one axisof the dissipator and spaced symmetrically either side of the other axisthereof so that the dis sipator effectively comprises two U-shapedbodies set one atop the other and joined in the regions 46. Thecolumnar-elements 38, which are made up of the legs of the two U-shapedbodies, are so shaped as to have a predisposition or preformed tendencytoward instability in a laterally outward or mutually separatingdirection when compressive load is applied to the dissipator along thelongitudinal centerline of the device parallel the elements 38.

In closer terms, the dissipator may be viewed as an elastomeric bodywhich is sufficiently rigid to perform through its various portionssubstantially like a linkage made up of a pair of links in each columnarelement 38 extending from corner primary hinge areas 48- at each end ofthe two columnar elements 38 and joined at a central primary hinge areaconstituted by the juncture regions 46. In FIG. 3, the designation ofpoints within regions 46 and 48- has reference to the centroids of theselocalized mass regions. In the central hinge areas 46, it is seen thatthe preferred embodiment employs local enlargements with preformedoutward bulge whereby the centroids 46 of such area are located eachlaterally outwardly of the two adjacent centroidal locations in cornerregions or areas 48. Accordingly, any

compressive loading applied across the width of base 40 and naturallyconcentrated largely to act longitudinally through the columnar elements38 will, by virtue of force equilibrium through the columnar elements 38will, by virtue of force equilibrium through the laterally spacedcentroids of areas 46 and 48, cause these columnar elements 38 to have apredisposition to laterally outward buckling.

Such outward buckling is resisted by the web 42 acting in tension. Theweb thus imparts column stability to columnar elements 38 in compressionand by suitable sizing of the thickness of the web in conjunction withthe selection of centroid location in areas 46 and 48, the load at whichthe columnar elements will buckle or fold may be easily dictated.

It is to be observed that the predisposition to the laterally outwardbuckling in elements 38 may be accomplished in other manners of shapingof the elements over their length. It is, however, believed preferablethat in any case there be a definite hinge area in the regions 46 midwaythe length of the columnar elements so that the generally tubular crosssection of the dissipator will collapse in a symmetrical manner underimpact force in the manner indicated in FIG. 5. In the illustratedembodiment, a single web 42 is shown extending directly between thesehinge regions 46 but itshould be appreciated that the single web definedby the two cavities 44 might be replaced by two or more webs locateddifferently along the lengths of the elements 38 but still operative tocontrol buckling resistance thereof and permit localized hinging orfolding thereof about specific hinge points generally at those shown at46 and 48.

FIG. 5 illustrates the folding action which takes place in theparticular configuration of the dissipator of this inventionundercompressive loading therein, about the hinge areas 46 and 48 of thecolumnar portions as shown in the FIG., with base portions 40 remainingrelatively undistorted. This lack of base distortion may be accomplishedif desired by stiffening members 50 embedded in the base portions, whichmembers aid in the rigid bolt attachment of the dissipators to the vehicle frame and bumper. However, additional energy dissipation may beavailable from allowing deformation of these base portions in a concavebulging by schemes of rigid attachment of the dissipators in the vehicleother than use of bolts 31 through the central region of the baseportions.

The web 42 is seen as having been caused substantial elongation ascolumnar elements 38 are folded about their hinge points to positionslaterally separated to the extent shown in FIG. 5, and to even furtherextent where the impact forces are at a maximum design level for thedissipator sufficient to bottom the base portions on the web 42.Following release of impact force on bumper l6, elasticity in web 42 andthe elasticity directly within the base portions 40 and columnarelements 38 serve to return the dissipator from its folded or collapsedcondition, such as indicated in FIG. 5, back to its normal unstressedcondition of FIG. 3.

It is to be appreciated also that in addition to the dimensional orshaping considerations leading to predictable buckling load, the lengthsof columns 38 and bases 40 are useful in controlling the deflection ofthe device. Thus, a shorter column and longer base requires lesselongation of web 42 into fully flattened condition, but reduces theviscoelastic energy dissipation therefrom. As indicated roughly in thedrawings, a column to base length ratio of 1.5 to 1 has provensatisfactory in use with certain elastomeric materials as specifiedbelow.

The energy of impact applied to bumper l6 and the several dissipators 26and 28 is substantially irreversibly absorbed or dissipated through theviscous and viscoelastic properties of the particular elastomericmaterial which is selected as suitable to particular applications ofthis invention, examples of which materials are given below. Theparticular physical configuration of the device of the inventionutilizes these effects to maximum advantage. By virtue of theconfiguration, the elastomeric body will sustain impact force loadingsof a very large magnitude which may be predetermined in accordance withthe predictable buckling tendencies of columnar elements 38 as above setforth. The buckling is accompanied by a predetermined or predictableamount of deflection in the device particularly the web thereof, asindicated in FIGS. 3 and 5. During the deflection these viscous andviscoelastic properties are focused to become operative for irreversibleabsorption or dissipation of the energy, yet are dimensionally limited.or controlled so as not to cause rupturing of the dissipator devicebody. Following release of the impact forces, the elastic property ofthe unruptured dissipator material becomes operative to relativelyslowly, without violent rebound from undissipated energy, return thedissipators and bumper 16 to original condition.

FIG. 7 is a force deflection graph generally indicating theseoperational attributes of the device. Beginning at the originrepresenting the unstressed configuration of FIG. 3, an impact force onbumper 16 applied to an individual dissipator would cause an initialdeflection of the dissipator body without buckling due principally to agenerally linear rate of elastic compression thereof rising with loaduntil the body experiences the condition represented generally at pointa, such point being the force loading at which columnar elements 38experience the onset of buckling in accordance with the predeterminationfactors discussed above. By virtue of the tensile resistance supplied byweb 42, the outward buckling of elements 38 is accompanied bysubstantial elongation of the web and the resistance thereto maintainsthe force level in the device generally at the buckling load untildeflection reaches the condition shown at b, whereat the base portions40 are incipiently bottomed out on web 42 as above described. Therefollows an additional compression of the entire dissipator body, asbetween the mounting flanges 30, until point e is reached representing agenerally maximum allowable deflection in the device. During suchdeflection the viscous and viscoelastic properties of the elastomericdissipator material serve to transform the applied kinetic energy andresulting deflection into material flow and molecular free energy orheat. This transformation or irreversible energy absorption isrepresented by the generally vertical portion of the curve betweenpoints 0 or d thereon. The energy dissipation takes place principally inweb 42 but derives also from the viscous and viscoelastic effects in theprimary hinge areas 46 and 48 and to yet lesser degrees in otheradjacent portions of the deflected dissipator. There then follows frompoint dthe elastic self-restoration of the dissipator to its originalcondition due to release of the remainder of the applied energy in thedissipator which has been retained as elastic distortion.

It is of course to be appreciated that the amount of energy dissipatedis that which is represented in footpounds or like units by theintegration of the curve or calculation of the amount of areatherewithin. Testing indicates that this energy dissipation can be ashigh as approximately percent of the energy which has been applied tothe dissipator.

The curve shown in FIG. 7 approximates those which result from dynamictesting of the dissipator involving the impacting thereon of a movingbody at a speed of up to 6.5 mph. Because of this dynamic or abruptapplication of impact energy, the threshold level of dissipator bucklingor deflection as at point a is raised considerably above that whichwould be experienced in a slow or static test. This is believed due todynamic strain or a natural stiffening or increase in the modulus of thematerial of columnar elements 38 under abruptly applied forces.

In testing of dissipator bodies structured generally in the crosssectional configuration of that shown in FIG. 3, wherein the ratio ofthe length of columnar elements 38 to the extent of base portion 40 isabout 1.5 to i, it has been found that web 42 will stretch duringcollapse to about percent of its normal length. This relatively highelongation must of course be accommodated in the selection of thematerial used along with the desired feature of high stiffness or highmodulus of elasticity. In some cases, where it is found that thematerial provides insufficient elongation property suitable torepetitious impact on the device, the ratio of height to base of thisrectangular configuration may have to be reduced.

Materials believed suitable for use in the dissipators in respect ofproper modulus of elasticity, tensile strength and elongation includenatural rubber, polychloroprene, butadiene-styrene copolymers,butadiene-acrylonitrile copolymers and solid polyurethane polymers.Highly satisfactory results have been found particularly with highdensity polyurethane material, which produced the dissipation resultsspecified hereinabove during dynamic testing.

Natural and synthetic rubber products offer higher elongation propertiessuitable to a very large number of impacts and less variation ofmaterial properties with temperature, but exhibit less stiffness.Accordingly, the use of rubber material advantageously to the principlesof this invention could involve modifications of the cross sectionalstructure shown in FIG. 3, particularly the addition of stiffeningplates of steel or the like molded in situ within columnar elements 38between each hinge area 48 and its adjacent central hinge area 46 to aidin the desired linkage-like collapse deriving from such relatively stiffcolumnar elements.

The use of four dissipators has been found to be generally necessary inbumper configurations such as that illustrated but where only ablade-type face or collision bar is used two dissipators may suffice,one at each of the opposite ends of the bumper. The stiffness propertiesof the solid polyurethane and like materials have been found sufficientto provide the sole support of the bumper on the vehicle frame. To avoidvibration or shake of the bumper 16 on the frame when the vehicletravels rough roads, it has been found advantageous to clamp or compressthe dissipators between the frame and bumper with a proper amountofdeflection or preload.'Where the vehicle to which the dissipators are tobe applied is among the heavier models and vertical jacking loads are tobe applied directly to the bumper 16 to change a flattire or the like,it may bedesirable to modify the installation of the dissipators so thatthe bumper is mounted on the frame principally by pivoted brackets orother means, but in such manner as to interpose the dissipators betweenthe bumper and frame in a manner wherein horizontal impact forces areapplied to the dissipators.

Having thus described this invention, what is claimed l. A reusableimpact energy dissipator for absorbing large amounts of kinetic energysubstantially irreversibly followed by self-restoration to an originalundeformed shape, said dissipator comprising a tubular body of highdensity urethane material having the properties of a high modulusof'elasticity, high tensile strength and high elongation, said tubularbody having at least a pair of cavities extending therethrough andaligned on a longitudinal center plane of said body and defining at eachside of said bodyan elongated columnar portion each integrally connectedat its opposite ends'with a pair of opposite elongated base portionsdisposed generally normal to said center plane, the rectangular'fourcorners of intersection between said columnar and base portions definingprimary hinge portions for deformation of said body with the centroidsof said corner hinge portions being aligned longitudinally andtransversely of said body, there being further defined in said bodybetween said cavities at least one tensile web extending with integralconnection between said columnar portions across said body generallyparallel to said base portions, said columnar portions each havingenlarged primary hinge portions midway their length, the centroid ofeach such primary hinge portion being spaced laterally outward of thetwo adjacent corner hinge portions so that said columnar elements haveleast buckling resistance under compression loading in a laterallyoutward direction whereby under predetermined impact forces appliedcompressively generally along said center plane said columnar elementsfold about the six mentioned primary hinge portions and said bodyforeshortens thereon and expands outwardly, said cavities being open ateach end of said body to prevent compression of any matter thereinduring reduction of volume of said cavities, said tensile web duringsuch fore-shortening undergoing substantial elongation and irreversibleenergy dissipating viscoelastic flow within the material thereof withoutrupture therein and operative upon release of such compression loadingto return the body to its undeformed shape, said corner and saidenlarged hinge portions also undergoing irreversible energy dissipatingviscoelastic flow without rupture during such foreshortening and beingoperative to return said body to itsoriginal undeformed shape followingrelease of said compression loading.

2. The energy dissipator recited in claim 1 wherein saidtensile w b etnds with, integtraL onnection between the en arge Inge portions 0 sancolumnar portions, said cavities comprising but two in number one eitherside of said tensile web.

3. The energy dissipator recited in claim 1 further including stiffeningmembers embodied within said base portions preventing gross distortionof the latter during said foreshortening deformation of said body.

4. In a vehicle including a structural portion adapted for'mountingthereon of a collision bumper bar, the combination comprising, acollision bumper bar extending transversely of said vehicle, at least apair of energy dissipating bumper mounts one disposed at each end ofsaid bumper bar, each said mount comprising a tubular body of highdensity urethane material having the properties of a high modulus ofelasticity, high tensile strength and high elongation, said tubular bodyhaving at least a pair of cavities extending therethrough and aligned ona longitudinal center plane of said body anddefining at each side ofsaid body an elongated columnar portion each connected at its oppositeends with a pair of opposite elongated base portions disposed generallynormal to said center plane, the rectangular four corners ofintersection between said columnar and base portions defining primaryhinge portions for deformation of said body with the centroids of saidcorner hinge portions being aligned longitudinally and transversely ofsaid body, there being further defined in said body between saidcavities at least one tensile web extending with integral connectionbetween said columnar portions across said body generallyparallel tosaid base portions, said columnar portions each having enlarged primaryhinge portions midway their length, the centroid of each such primaryhinge portion being spaced laterally outward of the two adjacent cornerhinge portions so that said columnar elements have least bucklingresistance under compression loading in a laterally outward directionwhereby under predetermined impact forces applied compressivelygenerally along said center plane said columnar elements fold about thesix mentioned primary hinge portions and said body foreshortens thereonand expands outwardly, said cavities being open at each end of said bodyto prevent compression of any matter therein during reduction of volumeof said cavities, said tensile web during such foreshortening undergoingsubstantial elongation and irreversible energy dissipating viscoelasticflow within the material thereof without rupture therein and operativeupon release of such compression loading to return the body to itsundeformed shape, said corner and said enlarged hinge portions alsoundergoing irreversibleenergy dissipating viscoelastic flow withoutrupture during such foreshortening and being operative to return saidbody to its original undeformed shape following release of saidcompression loading, a stiffening member embedded in each said baseportion, means interconnecting one of said base portions and itsstiffening member of each of said mounts on a respective end of saidbumper bar, and means interconnecting the other base portion and itsstiffening member of each said mount to said vehicle structural portion.

1. A reusable impact energy dissipator for absorbing large amounts ofkinetic energy substantially irreversibly followed by self-restorationto an original undeformed shape, said dissipator comprising a tubularbody of high density urethane material having the properties of a highmodulus of elasticity, high tensile strength and high elongation, saidtubular body having at least a pair of cavities extending therethroughand aligned on a longitudinal center plane of said body and defining ateach side of said body an elongated columnar portion each integrallyconnected at its opposite ends with a pair of opposite elongated baseportions disposed generally normal to said center plane, the rectangularfour corners of intersection between said columnar and base portionsdefining primary hinge portions for deformation of said body with thecentroids of said corner hinge portions being aligned longitudinally andtransversely of said body, there being further defined in said bodybetween said cavities at least one tensile web extending with integralconnection between said columnar portions Across said body generallyparallel to said base portions, said columnar portions each havingenlarged primary hinge portions midway their length, the centroid ofeach such primary hinge portion being spaced laterally outward of thetwo adjacent corner hinge portions so that said columnar elements haveleast buckling resistance under compression loading in a laterallyoutward direction whereby under predetermined impact forces appliedcompressively generally along said center plane said columnar elementsfold about the six mentioned primary hinge portions and said bodyforeshortens thereon and expands outwardly, said cavities being open ateach end of said body to prevent compression of any matter thereinduring reduction of volume of said cavities, said tensile web duringsuch foreshortening undergoing substantial elongation and irreversibleenergy dissipating viscoelastic flow within the material thereof withoutrupture therein and operative upon release of such compression loadingto return the body to its undeformed shape, said corner and saidenlarged hinge portions also undergoing irreversible energy dissipatingviscoelastic flow without rupture during such foreshortening and beingoperative to return said body to its original undeformed shape followingrelease of said compression loading.
 2. The energy dissipator recited inclaim 1 wherein said tensile web extends with integral connectionbetween the enlarged hinge portions of said columnar portions, saidcavities comprising but two in number one either side of said tensileweb.
 3. The energy dissipator recited in claim 1 further includingstiffening members embodied within said base portions preventing grossdistortion of the latter during said foreshortening deformation of saidbody.
 4. In a vehicle including a structural portion adapted formounting thereon of a collision bumper bar, the combination comprising,a collision bumper bar extending transversely of said vehicle, at leasta pair of energy dissipating bumper mounts one disposed at each end ofsaid bumper bar, each said mount comprising a tubular body of highdensity urethane material having the properties of a high modulus ofelasticity, high tensile strength and high elongation, said tubular bodyhaving at least a pair of cavities extending therethrough and aligned ona longitudinal center plane of said body and defining at each side ofsaid body an elongated columnar portion each connected at its oppositeends with a pair of opposite elongated base portions disposed generallynormal to said center plane, the rectangular four corners ofintersection between said columnar and base portions defining primaryhinge portions for deformation of said body with the centroids of saidcorner hinge portions being aligned longitudinally and transversely ofsaid body, there being further defined in said body between saidcavities at least one tensile web extending with integral connectionbetween said columnar portions across said body generally parallel tosaid base portions, said columnar portions each having enlarged primaryhinge portions midway their length, the centroid of each such primaryhinge portion being spaced laterally outward of the two adjacent cornerhinge portions so that said columnar elements have least bucklingresistance under compression loading in a laterally outward directionwhereby under predetermined impact forces applied compressivelygenerally along said center plane said columnar elements fold about thesix mentioned primary hinge portions and said body foreshortens thereonand expands outwardly, said cavities being open at each end of said bodyto prevent compression of any matter therein during reduction of volumeof said cavities, said tensile web during such foreshortening undergoingsubstantial elongation and irreversible energy dissipating viscoelasticflow within the material thereof without rupture therein and operativeupon release of such compression loading to return the body to itsundeformed shape, said corner and said enlarged hinge pOrtions alsoundergoing irreversible energy dissipating viscoelastic flow withoutrupture during such foreshortening and being operative to return saidbody to its original undeformed shape following release of saidcompression loading, a stiffening member embedded in each said baseportion, means interconnecting one of said base portions and itsstiffening member of each of said mounts on a respective end of saidbumper bar, and means interconnecting the other base portion and itsstiffening member of each said mount to said vehicle structural portion.